Determining the vehicle linear velocity in vehicles having all-wheel drive

Abstract

A method for determining the vehicle linear velocity of a vehicle having all-wheel drive, and which is equipped with a central lock and a vehicle controller to implement an ABS or ASR control. The vehicle linear velocity is able to be determined if a braking-pressure difference is adjusted at the wheels of an axle, and, in the case of an ABS control, the vehicle linear velocity is determined from the rotational speed of the wheel having the higher speed, and from the slip of this wheel, and, in the case of an ASR control, it is determined from the rotational speed of the wheel having the lower speed, and from the slip of this wheel.

What is claimed is: 
     
       1. A method for determining a vehicle linear velocity of a vehicle having all-wheel drive and a vehicle controller, the method comprising:
 adjusting a braking-pressure difference at two diametrically opposed wheels of an axle if an ABS or ASR controller is active; and 
 at least one of (i) calculating, in the case of an ABS control, the vehicle linear velocity from a rotational speed of a wheel having a higher speed, and from a slip of the wheel having the higher speed, and (ii) calculating, in the case of an ASR control, the vehicle linear velocity from a rotational speed of a wheel having a lower speed, and from a slip of the wheel having the lower speed; 
 wherein the braking-pressure difference is selected such that a friction of a differential gearing is overcome. 
 
     
     
       2. The method as recited in  claim 1 , wherein the vehicle velocity is determined according to the following equation: 
       
         
           
             
               
                 
                   v 
                   x 
                 
                 = 
                 
                   v 
                   
                     1 
                     - 
                     λ 
                   
                 
               
               , 
             
           
         
       
       and wherein v is the speed of the wheel having the higher speed in the case of ABS control or the wheel having the lower speed in the case of ASR control, and λ, being the slip of this wheel. 
     
     
       3. The method as recited in  claim 1 , wherein the slip is determined using real and simplified tire characteristic curves. 
     
     
       4. The method as recited in  claim 1 , wherein the axle is a rear axle. 
     
     
       5. The method as recited in  claim 1 , wherein one of a braking pressure and braking force is increased or decreased at one of the wheels in order to generate a braking-pressure difference. 
     
     
       6. A method for determining a vehicle linear velocity of a vehicle having all-wheel drive and a vehicle controller, the method comprising:
 adjusting a braking-pressure difference at two diametrically opposed wheels of an axle if an ABS or ASR controller is active; and 
 at least one of (i) calculating, in the case of an ABS control, the vehicle linear velocity from a rotational speed of a wheel having a higher speed, and from a slip of the wheel having the higher speed, and (ii) calculating, in the case of an ASR control, the vehicle linear velocity from a rotational speed of a wheel having a lower speed, and from a slip of the wheel having the lower speed; 
 wherein an operational sign of the braking-pressure difference is periodically reversed. 
 
     
     
       7. The method as recited in  claim 6 , wherein the vehicle velocity is determined according to the following equation: 
       
         
           
             
               
                 
                   v 
                   x 
                 
                 = 
                 
                   v 
                   
                     1 
                     - 
                     λ 
                   
                 
               
               , 
             
           
         
       
       and wherein v is the speed of the wheel having the higher speed in the case of ABS control or the wheel having the lower speed in the case of ASR control, and λ being the slip of this wheel. 
     
     
       8. The method as recited in  claim 6 , wherein the slip is determined using real and simplified tire characteristic curves. 
     
     
       9. The method as recited in  claim 6 , wherein the axle is a rear axle. 
     
     
       10. The method as recited in  claim 6 , wherein one of a braking pressure and braking force is increased or decreased at one of the wheels in order to generate a braking-pressure difference. 
     
     
       11. A control device for a vehicle having all-wheel drive, comprising:
 a control arrangement configured to adjust a braking-pressure at two diametrically opposed wheels of an axle, 
 wherein: 
 the control device is configured to determine a vehicle linear velocity from a wheel having a higher speed and from a slip the wheel having the higher speed, in the case of ABS control, and to determine the vehicle linear velocity from a wheel having a lower speed and from a slip of the wheel having the lower speed, in the case of ASR control; and 
 the braking-pressure difference is selected such that a friction of a differential gearing is overcome. 
 
     
     
       12. The device as recited in  claim 11 , wherein the vehicle velocity is determined according to the following equation: 
       
         
           
             
               
                 
                   v 
                   x 
                 
                 = 
                 
                   v 
                   
                     1 
                     - 
                     λ 
                   
                 
               
               , 
             
           
         
       
       and wherein v is the speed of the wheel having the higher speed in the case of ABS control or the wheel having the lower speed in the case of ASR control, and λ being the slip of this wheel. 
     
     
       13. The device as recited in  claim 11 , wherein the axle is a rear axle. 
     
     
       14. The device as recited in  claim 11 , wherein one of a braking pressure and braking force is increased or decreased at one of the wheels in order to generate a braking-pressure difference. 
     
     
       15. The device as recited in  claim 11 , wherein an operational sign of the braking-pressure difference is periodically reversed. 
     
     
       16. The device as recited in  claim 11 , wherein the braking-pressure difference is regulated. 
     
     
       17. The device as recited in  claim 11 , wherein an operational sign of the braking-pressure difference is periodically reversed, and wherein the braking-pressure difference is regulated.